The present invention relates to a method for reducing the friction exhibited by an aqueous liquid during flow and to the aqueous liquid systems having such reduced friction.
In the flow of an aqueous liquid through a conduit, energy is required to overcome the friction created by the turbulence of the liquid flowing through the conduit. In many operations such as industrial applications, particularly those operations in which the velocity of the flowing aqueous liquid exceeds the limit required for smooth laminar flow (e.g., well fracturing treatments or the rapid movement of liquids for considerable distances), substantial expenditures of energy are required to overcome the friction losses. A reduction in the friction loss exhibited by a flowing aqueous liquid would permit lower amounts of energy expenditures and/or increased flow using the same energy.
Heretofore, various alternatives have been proposed to reduce the friction loss exhibited by a flowing aqueous liquid. For example, water-soluble, high molecular weight polymers such as a polymer of a monoalkenyl aromatic sulfonate (e.g., styrene sulfonic acid) or a polymer of a carboxamide (e.g., acrylamide) are known to reduce friction loss when added to an aqueous liquid in small amounts. See, for example, U.S. Pat. Nos. 3,023,760; 3,562,226 and 3,572,354. Unfortunately, the aqueous liquid systems containing the high molecular weight polymers are not shear stable, i.e., the friction reduction exhibited by the liquid containing said polymer is substantially and permanently lost when subjected to high shear.
Friction losses in a flowing aqueous liquid have also been reduced by the addition of a surfactant which imparts viscoelastic properties to the aqueous liquid. For example, U.S. Pat. No. 3,361,213 to Savins teaches that an alkali metal soap of a fatty acid, e.g., sodium oleate, in combination with a strong electrolyte will reduce the friction of an aqueous liquid. Similarly, Savins discloses that (1) an ammonium soap of a fatty acid will reduce the friction losses exhibited by an aqueous liquid containing a weak electrolyte and (2) a substituted ammonium soap of a fatty acid will reduce the friction losses of an aqueous liquid containing no electrolyte. Other viscoelastic surfactants such as 2-naphthol in combination with cetyl trimethyl ammonium bromide are also known to be useful as friction reducing agents. Although such viscoelastic materials often reduce the friction exhibited by an aqueous liquid flowing through a conduit, further reductions in friction over broad flow ranges are often desired, particularly in those operations wherein relatively large amounts of aqueous fluid are to be pumped over long distances.
In view of the aforementioned deficiencies of the prior art, it is highly desirable to further reduce the friction losses exhibited by a flowing aqueous liquid.